1. Field of the Invention
The present invention relates to control systems in series with an external load and an external source of electricity so as to energize and de-energize the external load with the external source of electricity depending upon the values of a plurality of sense parameters.
2. Description of the Prior Art
Although there are several prior art patents that disclose the use of electronic switches to effectively complete the connection of an external load to an external source of electricity, none of the prior art patents disclose a control system for sensing the combination of a plurality of external parameters and to thereby control energization and de-energization of the load in response to this combination of parameters by a control system in series with the external load and the external source of electricity. Thus, in U.S. Pat. No. 3,558,996, Mitchell, a circuit is disclosed in which a silicon controlled rectifier shorts out a full-wave bridge but which does not sense external parameters. U.S. Pat. Nos. 3,597,662, Gary, and 3,584,263, Thompson, also use a thyristor to energize an external device but do not disclose the use of remote sensors and control circuitry to energize a thyristor upon the external parameters reaching predetermined levels. Similarly, U.S. Pat. No. 3,553,535, Weber, does not teach the use of control circuitry to drive an electronic switch in response to externally sensed conditions.
Although other U.S. Patents disclose the electrical shorting of a full-wave rectifier bridge by a silicon controlled rectifier, none of these U.S. Patents disclose a control system in series with an external source of electricity and an external load so as to control the energization and de-energization of the load in response to the combination of a plurality of external sensed parameters. Thus, U.S. Pat. No. 3,818,247, Chambers et al, disclosed the use of a silicon controlled rectifier to control a load in response to a sensed condition, but the device is not in series with an external source of electricity. U.S. Pat. No. 3,818,183, Masson, discloses an electronic temperature control system utilizing an electronic switch but the disclosed system only senses one parameter, temperature. U.S. Pat. Nos. 3,708,738, Crawford et al, 3,691,404, Sweigert, Jr., 3,629,681, Gurwicz, 3,486,105, Breniere, 3,440,517, Page et al, 3,392,626, Miller et al, 3,365,654, Vollrath, 3,231,812, Paley, 3,331,013, Cunningham, and 3,146,392, Sylvan, all disclose electronic circuits utilizing a full-wave rectifier bridge and the effective shorting out of this bridge by an electronic switch, but none of these patents disclose the use of external sensors to control the operation of the electronic switch so as to activate the external load. U.S. Pat. 3,336,524, Healey also utilizes a full-wave bridge but this bridge is not in series with the source of electricity, and the electronic switches do not operate by sensing external parameters.
Although U.S. Pat. 3,365,654, Johnston discloses a full-wave bridge to control activation of a load in series with a source of electricity in response to an external sensor, only one sensor is disclosed and, in addition, the circuit is used for controlling the mean electrical power fed to a load rather than its activation or deactivation. Furthermore, Johnson utilizes an external oscillator for a portion of its control circuitry which incorporates a temperature sensing resistor. Thus, this portion of the control circuitry is not in series with the source of external electricity and the external load as is the present invention.
U.S. Pat. No. 3,783,368, Dosch et al, also discloses a control system in series with a source of external electricity and an external load so as to control the power to the external load. This patent discloses the use of a single sensor so as to control the average power to the external load. The use of a hysteresis effect for activation of the load is not disclosed and indeed, the purpose for the activation of the load is for controlling the duty cycle of the load. The present invention is not concerned with the varying duty cycle of the external load but its activation in response to a plurality of external sensed parameters. The activation of the external load of the present invention is thus used to control an external device such as a furnace, so as to maintain the furnace in operation until the external load is de-energized. Thus, the present invention is an on-off type of controller, rather than a proportional type controller disclosed in Dosch.